Rolling element thrust bearings have a pair of generally identical races that are assembled by pushing them axially together to capture a complement of bearing elements between the inner surfaces of the races. The race inner surfaces may be flat, but more often each has a trough like pathway that receives the bearing elements. Before installation, a retention structure may prevent the races for separating. After installation, of course, the retention structure is redundant, as the thrust forces push the races together, and the bearing elements keep the races spaced axially apart. It is desirable that the inboard and outboard sides of the bearing elements be sealed, both to retain lubricant and exclude contaminants.
A number of different structures have been proposed for sealing such bearings. Often, a pair of sealing lands is provided on each race, one inboard and one outboard of the pathway, which are maintained in axially spaced relation by the bearing elements. The lands may be a flat annular surfaces, or just that part of the race inner surface that borders the pathway. A seal is captured between each pair of opposed sealing lands to seal the bearing elements. A typical example of such seals is a pair of separate rings, as may be seen at 90 and 92 in FIG. 2 of U.S. Pat. No. 4,497,523 to Lederman, assigned to the assignee of the subject invention. Another example of a pair of separate seals may be seen at 48 and 46 in FIG. 1 of U.S. Pat. No. 4,708,497 to Lederman, also assigned to the assignee of the current invention, in which the seals also act to hold the races together.
While separate seals provide complete, rigorous sealing, they must be separately manufactured and assembled, which is costly in terms of numbers of parts and handling. One means of eliminating separate seals may be seen in U.S. Pat. No. 4,541,744 to Lederman, also assigned to the assignee of the invention, where a one piece molded cage prevents the races from pulling apart and also provides a non rubbing, labyrinth seal. This is useful in environments where absolutely rigorous sealing isn't necessary. An example of a design approach that eliminates separate seals, but still attempts to provide the rigorous sealing that separate seals would, may be seen in U.S. Pat. No. 3,414,341 to Murphy. There, seal lips are integrally molded to the cage so as to rub on the inner surface of each race. An inherent drawback of integrating the seal lips with the cage is that they are then forced to rotate with, and about the axis of, the rolling elements. Separate seals have the ability to follow their own path of least resistance between the seal lands, floating axially and raidally between the lands within limits, or sticking intermittently to one land and rubbing on the other. Being able to move independently, separate seals ahve the ability to seal most efficiently, finding an equilibrium, which seals that are tied to the cage cannot. A practical drawback of an integral cage-seal unit is that cages are molded from hard plastics, which are not particularly good at conforming to race surfaces. Murphy cantilevers the sealing lips to the cage to create some flexibility, but this also creates an undercut relative to the cage axis that would make it difficult to mold with a single pair of axially parting molds, known as by pass molding.